Photographic materials



Patent ed Sept. 12, 19,44

UNITED "STATES PATENT orricsi Edward Titli figlffrrsiignor to EastmanKodak Company, Rochester, N. Y., a I I corporation of New Jersey I NoDrawing. Application August 19, 1941, Serial '8 Claims.

(a) Silver chloride is naturally more contrasty than silver bromide.

(b) Silver chloride develops much more rapidly (usually 20 to 40 secs.)than silver bromide (usually 1 /2 to 2 mins.)

If the brightest possible print with good transparency in the shadowsare required from flat negatives, it is customary to use silver chloridewhich is superior to silver bromide in this particularrespect. On'theother hand, in view of (a) mentioned above, very soft prints aremore easily made on silver bromide paper.

It has been the practice .of all photographic manufacturers for morethantwenty years to sell numerous different sensitive papers.

Even as long ago as 1912 in British Specification-No. 15,054, Fischerproposed to make a In Great Britain September 3,

judge the development and readjust the exposure ,both as to amount andcolour of light if it was found to be incorrect the first time. For exifthe exposure has been too great, say double the correct exposure, thenwhen development is cut short in an endeavour to save the, print frombeing wasted, the contrast obtained is much too high which would nothave occurred when using.

ordinary single emulsion papers. Moreover, it is diflicult, in factusually impossible, to obtaina satisfactory printif development is cutshort as can be done in the case of standard single emuls ion papers,and which is in fact veryfrequently done to avoid waste when makingprints. Home the user is compelled to learn a new technique of judgingthe making of prints-by visual inspection.

Moreover, if the emulsions are coated as superposed layers, theimagewhich develops in the lower emulsion layer is, during development,considerably'obscured by the upper emulsionlayer and, as seen from abovein the case of photographic paper, the highlights or shadows,whichphotographic sensitive paper by mixing or coating one overthe othertwo emulsions giving differing contrasts under the same developmentconditions but with differing coloured lights for exposure. This resultcan be achieved'by using silverv chloride which as indicated above,lends itself to making a contrasty emulsion in conjunction with silverbromide which lends itself to making a soft emulsion. In fact, in anendeavour to produce such a variable contrast sensitive paper, it has'been proposed by Renwick in U. S. Patent No. 2,202,026 to mirror coatin separate layers, a dye-sensitised contrasty silver chloride emulsionand an ordinary soft silver bro-' mideor chloro bromide emulsion.

This method suffers from the serious disadvantage of giving a sensitivematerial which when exposed for different contrasts gives con-'siderable inconvenience in processing. When printing most negativeswhich do not fall at the absolute extremes of contrast (i. e. fullyvsoft or fully contrasty) where both emulsions come into play to varyingdegrees, the relation between therates of appearance of the highlightsand the heavy shadows in the same print is distorted, and moreover toadd to the difficulty, differs from one negative to another. This makesit difficult to tages referred to such as the restricted choice of vever develop first in the lower layer are obscured and give again anunpleasant and inconvenient rate of appearance of the different parts ofthe image and also fromone kind of negativeto another, especially in thecase of the large bulk of negatives which print between the extremeswhere both emulsions areutilised in varying degrees, all of which is ofcourse additional to the effects already mentioned as resulting fromusing different halides. Hencewhile the use of the same halides insuperposed layers overcomes some disadvantages it does not overcome .allof them.

It follows that inall the above proposals difliculty is entailed inattempting to develop by inspection to say nothing of ,the otherdisadvanconvenient developingsolutions and in particular I am not awareof any proposal to overcome this difliculty of inspection development.

It is an object of my inventionto produce a sensitive photographic paperwhich is eminently suitable for development by inspection as well ashaving other advantages, such as ease of making a mixture which gives,uniform image colours and uniform times of development over the wholerange of contrasts.

According to my invention I employ a mixture of an emulsion of a silverhalide which is optidescribe.

cally sensitised to a region of the spectrum and another emulsion of thesame halide but of different contrast which has its maximum sensitivityin another region of the spectrum whereby the mixture gives a differencein gradation of at least 2.5, the lowest gradation being below 1.8,

by exposing .tolights of ditlerent colours.- I may make both emulsionsof silver bromide or both of silver chloride, or even of chlorobromide,providing the halide compositions of the two emm sions are for allpractical purposes the same: a

I shallnow refer to various forms of my invention, each of whichachieves a-special object. Another disadvantage of'the use of halides isthatit is not possible to make a satis factory sensitive paper which issufliciently hightised that its natural sensitivity is sufliciently low.If the use of the natural sensitivity in this way could beavoided awider scope would be permitted in the production of the two emulsions ofthe mixture. I am not aware of any prior P p sal to avoid using thenatural sensitivity in thi way while atthe same time the material can beproowith a sharpEcutoif at say 580 dmerem, l5

: In all forms" of my invention I preferably emly sensitive for use invery rapidly operating Ina- P chines or where only a weak light exposureis possible. According to a special form of my invention'" this dimcultyis overcome by employing -a mixture of two silver bromide emulsions.

For some purposes it is desired to make a series -of. prints fromvarious negatives with a'very high a degree of brilliance and clarity."This was not achieved in the prior proposals of using a silver chlorideemulsion mixed with a silverbromide emulsion, since the images formed.in the silver chloride emulsion are-more brilliant than those formedinthesilver bromide emulsion. f-According toanother special form of myin- =vention I achievethisobject by employing'a mixture oftwosilverchlorideemulsions. I *If 'onee-mulsion is sensitised-to green andthe -"other is not sensitised. such a combination can- 1 not beprocessed in a yellow or yellowish-green or orange'light but must beprocessedin the more inconvenient red light. Sometimesthis does notmatter, but, for some purpossit-isuridoubtedly inconvenient. This isovercome, as well as all the disadvantagesol' prior proposals by'a,pre-' ferred form of my invention which I shall now essed in an orangeor light red light. I achieve this desirable result in a preferred formof using two silver chloride-emulsions in which both emulsion areoptically sensitised, one with a maximum at about 470 m and the other atabout550 ma Ijshallno'w describe the ways of performing the severalforms of my invention referred to above.

ploy' one emulsion which gives a gradation (measured as hereindescribed) less than 1.8 and the other emulsion which gives a gradationof at least 2.5 greater than that of the other emulsion and 'ofwhich oneof such emulsionslhereafter referredto as the former emulsion) issensitised to haveitsmaximum speed at least 60. m further towards thelongwavelengths than the maximum speed of the other of such emulsions,the speed of the former emulsion measured at about the wavelength of themaximum speedof theother emu1 "sion being not greater than hair thespeed or the other emulsion measured at the same'f wavelengths, whilemeasured at about the wavelength of maximum speed of the former emulsionthe speed thereof is at least twice the speed of the other emulsion. Formost purposes .it is preferable that both emulsions should besubstantially insensitive to wavelengths beyond 600 m The saidgradations are tobe measured by means of 7 light of about the-wavelength(as herein defined) In this preferred form which exhibit these specialfurther advantages I employ a silver chloride emulsion which hasnotbeenspecially u tically sensitised, and therefore'has a natural sensitivitywhich-is high at- 390v m withv a silver 1 chloride emulsion which hasbeen sensitised to have its-maximum optical sensitisation at about 520 mor less but preferably between 420 and 490 m for example 4'70 m with alow natural'sensitivity. When such maximum isat about 520 im thematerial: can be processedv in an orange light, but when it isabout47011111 it can be processed inarelatively brightyellow. I

My invention achieves aspecial advantage in, respect of producing warmtone prints with the same developing solutions containing largequantities of a restrainer both by visual inspec without. The use ofdifferent halides renders it extremely diflicult to obtain satisfactoryor at least similar brown or :warm-toned prints over the whole range ofcontrasts. Even the use of a silver chlorobromide emulsion as proposedby Renwick does not give satisfactory warm tone over 1 the whole rangeof contrasts. because "he mixes it with a silver chloride emulsion, andin fact I am not aware of any prior proposals to enable such prints to bmade.

I achieved this result in another special form of tionand Q of maximumspeed of the emulsion concerned.

WhereI refer herein to about a certain wavelength, I mean the range ofwavelengths covering 40 m each side thereof. 'To ascertain thewavelength of maximum speed there should be employed-a spectrogram madeby-using a, neutral wedgewith a tungsten filament, at 2700K as the lightsource,,and wavelengths below 390 m are excludedirom such measurements.1

I By the term silver bromide emulsion as used herein, I mean an emulsionwhich consists of at least 90% of AgBr based on the total silver halide.

By the tenn "silver chloride emulsion I means an emulsion which consistsof at least 90% iAgCl based on the total silver halide.

By thetermsilver-chloro-bromide emulsion wherever used herein Imeansilver-halide emulsions which contain over 10% and less than 90% (butpreferably over 30% and lessthan of 1 silver chloride based on the totalsilver halide. It is'desirable that the percentage silver chloridecontent of the two emulsion should not differ by more than 25, butpreferably not more than 10.

' Itis the practice to add sometimes some silver iodide to silverbromide, silver chloride and silverchloro-bromide emulsions, and suchemulsions are included within the terms of the present invention.

In order to produce a sensitive photographic element of the greatestconvenience. and simmy invention by employing two silver chlorobromideemulsions as will be described hereinafter.

All the above methods referred to, make use of the natural sensitivityof one emulsion, hence it is important to have the other emulsion sosensiplicity in use for most purposes (i. e. with most negativescommonly met in practice) I have sions'and the'optically sensitising dyeshould be found'that it is preferable that the coated emulso chosen thatthe speed in the blue region of the non-optically sensitised bluesensitive emulsion should beat least 1.8 (and preferably at least twice)the speed of the optically sensitised emulsion in the blue region, whilethe speed of the optically sensitised emulsion in the green to yellowregion should be between one-third and one-anda-quarter (preferablybetween three quarters and one-and-a-quarter) times the speed of thenon-optically sensitised emulsion in the blue region and the gradationof the non-optically sensitised emulsion in the blue portion should bebetween 0.8 and 1.8 (preferably between 1.0 and 1.6) while the gradationof the optically sensitised emulsion in the yellow to green region ofthe spectrum should be at least 2.5 greater (preferably 3.5 greater). Itis usually desirable that both emulsions be substantially insensitivebeyond 600 mu.

Usually the gradation of the optically sensitised emulsion will not bemore than 7.

All speeds herein referred to are measured by taking theexposurenecessary to give a density of 1.0.

Whenever I refer herein to the gradation of an emulsion I mean theaverage slope of the characteristic H. & D. curve between densities of0.4 to 1.6.

It is to be understood that when the emulsions are to be coated on anopaque support such as white paper, the density measurements which aremade to arrive at the aforesaid measurements are to be done by reflectedlight.

In all measurements referred'to or implied herein, development is doneat 68 1. for 1 /2 minutes with the following solution:

Metol grams- 2.2 NazSOs cryst do.. 150.0 Hydroquinone do 17.0 NazCOacryst -..q do 175.0 KBr. -do 2.8 Water ccs 1,000.

This solution is diluted with an equal part of water, for use.

Whenever I refer herein to the various characteristics (including speedand gamma) of each emulsion I mean when measured on the emulsion coatedas a layer by itself at a quantity per square foot which is the same asis used for that emulsion in the composite emulsion layer.

The measurements specifically referred to as in the blue portion of thespectrum are made byv exposing to a tungsten light (27003000 K) througha Wratten No. 47A filter, and in the green to yellow portion of thespectrum by exposing to sfiilich a tungsten light through a Wratten No.5

ter.

Preferably the non-optically sensitised blue sensitive emulsion shouldbe one having a characteristic H & D curve whose straight portion isas'long as possible.

For the. emulsion or emulsions which are optically sensitised there maybe used one or more sensitising dyes, and since the emulsions are to bemixed, such dyes must be incorporated in that emulsion before it ismixed with the non-optically sensitised emulsion in such manner thatafter the emulsions are mixed, any tendency of the dye or dyes to wanderfrom the one emulsion to the other is avoided or minimised for example,by adopting the procedure described in my application Serial No.387,437. The procedure described in the co-pending application of EdwardB. Knott and myself Serial No. 391,375 may be utilised in the productionof the optically. sensitised emulsion. Dyes having little tendency towander are described in the co-pending application of Leslie G. S.Brooker Serial No. 321,370 filed March 1, 1940.

' Example 1 danine or St (2-ethyl-1 (2) -benzoxazolylidene) ethylidenel-3-nh e p t y l-l-phenylQ-thiohydantoin. The emulsion so opticallysensitised had a speed in the blue region of 2.0 with a speed in thegreen to yellow of 5.7 and gradation in the green to yellow of 5.5. Thisemulsion was allowed to stand while adding soft lac to the nonopticallysensitised emulsion. This latter was a silver bromide emulsion(containing 3% silver iodide calculated on the total silver halidecontent but free from silver chloride) having aspeed in the blue regionof 5.4 and a gradation 1.5. To an amount of this emulsion made from 200grams of silver nitrate there was added 500 cos. of ethyl alcoholcontaining 10'grams of soft lac (at 35 C.).' The emulsions at 35 C. weremixed and coated immediately on a paper support.

Example 2 An optically sensitised emulsion of silver bromide without anyother silver halide was prepared as follows; take an amount of anemulsion giving a high gradation and made from 200 grams of silvernitrate and immediately after formation of the silver bromide there wasadded 0.03 gram of the second named dye of Example 1. This was ripenedat 40 C. for ten minutes; then allowed to set and washed; more gelatinewas added and then digested at 55 C. for 30 minutes.

The emulsion so prepared had a speed in the blue of 1.0 with a speed inthe green to yellow of 2.7 and gradation in the green to yellow of 4.4.

A non-optically sensitised emulsion for mixing therewith was prepared soas tohave a speed in the blue region of 4.7 and a gradation of 1.3. Thetwo emulsions were mixed and coated immediately on a paper support.

Example 3 A bromide emulsion giving a high gradation and containing theequivalent of 200 grams of silver nitrate was adjusted to a pH of 7 andsensitised with 0.05 gram of 3-ethyl-5-(2-ethyl-1-benzoxazylidene-ethylidene) 1-phenyl-2-thiohy dantoin and allowed tostand for 30-minutes at- 35" C. A suspension containing 50 grams ofmagnesium hydroxide was then added, followed by a 5% alcoholic solutionof 50 grams of soft lac resin, and then followed by addition of 50 gramsof potassium chloride. The product was then kept at 35 C. until thespeed of the emulsion had reached the required figure (say minutes). Theemulsion so prepared had a speed in the blue of 1.5 with a speed in thegreen to yellow of 3.0 and gradation in the green to yellow of 4.5. Thesame quantities of magnesium hydroxide and resin were added to a bromideemulsion to have a speed in the blue of 4.0 and a gradation of 1.2.These two emulsions were port. I

30 C. and coated.

Erample 4 of silver bromide and 1% of silver iodide calculated on itstotal silver halide content and having a speed in the violet of 0.3 anda gradation of 1.5. The two emulsions were mixed in equal proportions at30 C. and coated.

Example 5 An amount of a silver chloride emulsion was made from 200grams of silver nitrate and immediately after formation of the silverchloride there was added 0.1 gram of the same dye as used in Example 2.This emulsion was then ripened at about 60 C. for about v40 minutes andthen more gelatine added. The emulsion so prepared had a speed in theviolet of 0.1 with a speed in the green to yellow of 0.8 and gradationin the green to yellow of 5.0. Also there was prepared a silver chlorideemulsion in like manner except using the dye3-n-heptyl-5(1-methyl-3-5-naphthoxazolylidene) rhodanine; this emulsionhad a speed in the violet of 0.3, and in the blue of 1.1 with'agradation in the blue of 1.4. The two emulsions were mixed in equalproportions at Example 6 An amount of a silver chloro-bromide emulsionof 50% silver-chloride and 0 to.%% silver-iodide content (the remainderthus being silver bromide) was made from 200 grams of silver nitrate andimmediately after formation of the silver halide 0.1 gram of the samedye as used in Example 2 was added. This was ripened at about 60 C.

' for about 40 minutes and then more gelatine added, allowed to set andwashed well. The emulsion so prepared had a speed in the blue to violetof 0.2 with a speed in the green to yellow of 0.7 and gradation in thegreen to yellow of 5.0. There was also prepared a silver chloro-bromideemulsion of the same halide composition which was not opticallysensitised but had a speed in the blue to violet of 0.8 and gradation of1.4. These two emulsions were mixed in equal proportions at about 30 C.and coated on paper.

I claim:

1. A photographic printing material for making prints of substantiallythe same contrast and same density range from negatives of widely.differing contrasts containing a sensitive layer comprising a mixture oftwo emulsions of the same silver halide, each emulsion being present inquantity suflicient to give a density of at least 1.6, at least oneemulsion being optically sensitized before mixing the emulsions so thatafter mixing the two emulsions their maximum sensitivities lie indiiferent spectral regions, one emulsion hava ing in its region ofmaximum sensitivity before mixing a gradation of less than 1.8 over adensity range of 0.4 to 1.6 and the other emulsion having inits regionof maximum sensitivity before mixing a gradation at least 2.5 greaterthan that of the first emulsion over a density range of 0.4 to 1.6.

2. A photographic printing material for making prints of substantiallythe same contrast and 7 prising a mixture of two silver bromideemulsions, each emulsion being present in quantity suificient to give adensity of at least 1.6, at least one emulsion being opticallysensitized before mixing the emulsions so that after mixing the twoemulsions their maximum sensitivities lie in different spectral regions,one emulsion having in its region of maximum sensitivity before mixing agradation of less than 1.8 over a density range of 0.4 to 1.6 and theother emulsion having in its region of maximum sensitivity before mixinga gradation at least 2.5 greater than that of the first emulsion over adensity range of 0.4 to 1.6. V

3. A. photographic printing material for making prints of substantiallythe same contrast and same density range from negatives of widelydiffering contrasts containing a sensitive layer comprising a mixture oftwo silver chloride emulof 0.4 to 1.6 and the other emulsion having inits region of maximum sensitivity before mixing a gradation at least 2.5greater than that of the first emulsion over a density range of 0.4 to1.6.

4. A photographic printing material for making prints of substantiallythe same contrast and the same density range from negatives of widelydiffering contrasts containing a sensitive layer comprising a mixture oftwo silver chlorobromide emulsions, each emulsion being present inquantity sufficient to give a density of at least 1.6, at least oneemulsion being optically sensitized before mixing the emulsions so thatafter mixing the two emulsions their maximum sensitivities lie indilferent spectral regions, one emulsion having in its region of maximumsensitivity before mixing a gradation of less than 1.8 over a densityrange of 0.4 to 1.6 and the other emulsion having in its region ofmaximum sensitivity before mixing a gradation at least 2.5 greater thanthat of the first emulsion over a density range of 0.4 to 1.6.

5. A photographic printing material for making prints of substantiallythe same contrast and same density range from negatives of widelydiffering contrasts containing a sensitive layer comprising a mixture ofa silver chlorobromide emulsion whose chloride content lies between 10per cent and 25 per cent of the total halide in the emulsion and anothersilver chlorobromide emulsion Whose chloride content lies between 10 percent and 25 per cent of the total halide in the emulsion, each emulsionbeing present in quantity suflicient to give a density of at least 1.6,at leastone emulsion being optically sensitized before mixing theemulsions so that after mixing the two emulsions their maximumsensitivities lie in different spectral regions, One emulsionhavemulsion being optically sensitized with a maximum at about 4'70-"mand the other emulsion being not optically sensitized, the one emulsionhaving in its region of maximum sensitivity before mixing a gradation ofless than 1.8 over a density range of 0.4 to 1.6 and the other emulsionhaving in its region of maximum sensitivity before mixing a gradation ofat least 2.5 greater than that of the first emulsion over a densityrange of 0.4 to 1.6.

7. A photographic printing material for making prints of substantiallythe same contrast and same density range from negatives of widelydiffering contrasts containing a sensitive layer comprising a mixture oftwo silver chloride emulsions, each emulsion being present in quantitysufiicient to give a density of at least 1.6, the one emulsion beingoptically sensitized with a maximum at about 550 m and the otheremulsion being optically sensitized. with a maximum at about 470 ml, theother emulsion having in its region of maximum sensitivity before mixinga gradation of less than 1.8 over a density range of 0.4 to 1.6 and theother emulsion having in its region of maximum sensitivity before mixinga gradation at least 2.5 greater than that of the first emulsion over adensity range of 0.4 to 1.6.

8. A photographic printing material for making prints of substantiallythe same contrast and same density range from negatives of widelydiffering contrasts containing a sensitive layer comprising ,a mixtureof two emulsions of the samev silver halide, each emulsion being presentin quantity sufllcient to give a density of at least 1.6, at least oneemulsion being optically sensitized before mixing the emulsions so thatafter mixing the 'two emulsions their maximum sensitivities lie indifierent spectral regions, the one emulsion having in its region ofmaximum sensitivity before mixing a gradation of less than 1.8 overadensity range of 0.4 to 1.6 and the other emulsion having in its regionof maximum sensitivity before mixing a gradation at-least 2.5 greaterthan that of the first emulsion over a density range of 0.4 to 1.6, theone emulsion being optically sensitized to have its maximum speed atleast m further toward the longer wavelengths than the maximum speed ofthe other emulsion, the speed of the first emulsion measured at aboutthe wavelength ,of the maximum speed of the other emulsion being notgreater than half the speed of the other emulsion measured at the samewavelength, while measured at about the wavelength of the maximum speedof the first emulsion, the speed of the first emulsion is at least twicethe speed of the other emulsion, both emulsions being substantiallyinsensitive to wavelengths beyond 600 m EDWARD P. DAVEY.

